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CIRCULATION, BLOOD AND GLANDS 235
investigation permits of our drawing certain definite conclusions. It is a remarkable fact, as I stated on a former occasion with regard to mv results with the
Anthropoidea—and this applies as well to other groups of animals—that a common property has persisted in the bloods of certain groups of animals throughout the ages which have elapsed during their evolution from a common ancestor, and this in spite of differences of food and habits of life."
The precipitin test is carried out as follows: A rabbit receives at intervals five or six intravenous injections of 5 c.c. of human blood serum. Seven to twelve davs after
the last injection it is killed and bled. The blood is allowed to coagulate, and the serum is collected and stored in small tubes with sealed ends. A few drops of chloroform are added to each for preserving purposes* As human blood serum is used for injections the rabbit serum is known as an anti-human serum, but anti-chimpanzee, anti-orang, anti-fowl and other sera are also prepared in a similar way. If fresh human serum is added to one of the tubes a thick precipitate is thrown down; and if the sera of the animals closely related to Man are added to successive tubes a precipitate is formed, but it is not so thick. Similarly an anti-chimpanzee serum yields a precipitate if the blood of Man and the other Anthropoids is added to it. After carrying out some hundreds of tests, Nuttall came to the following conclusions: (1) There is a close relationship between the Hominidse and Simiidse, and a more distant relationship with the Cercopithecidse; (2) the bloods of the Cebidse and Hapalidse give poor reactions with those of the preceding families; (3) the anti-sera for all the